Re: [oss-drivers] Re: [PATCH/RFC net-next 1/2] flow dissector: ND support

Wed, Feb 08, 2017 at 08:10:06PM CET, tom@herbertland.com wrote:

On Wed, Feb 8, 2017 at 10:54 AM, David Miller [off-list ref] wrote:

quoted

From: Tom Herbert <redacted>
Date: Wed, 8 Feb 2017 10:33:46 -0800

quoted

On Wed, Feb 8, 2017 at 1:28 AM, Simon Horman [off-list ref] wrote:

quoted

I think the above paragraph gets back to Tom's original question regarding
making things more complex just for OvS (use-cases). Possibly ND is an edge
case even for OvS and on reflection my timing for posting it seems to have
been less than ideal.

If it wasn't ND it would be something else... with all the activity
happening in networking features and HW this is a timely discussion.
Flow dissector presents a good example of a function that might become
a dumping ground for an endless stream of features if we don't figure
out how exercise some restraint.

I agree on most points.

But, I would say that in this specific case, since we have ARP support in
there already it behooves us to support the ipv6 side in the form of ND
too.

Then we can put a line in the sand and say that future feature additions
in this area require serious discussion.

Ok Tom?

Right, ND is okay on the basis that we already have ARP (although I
still may grumble from time to time that ARP, ND, and ICMP are being
identified as flows ;-) ).

I think there are two projects in the are that someone, maybe an
aspiring kernel network developer, might want to look into if they
have the time:

- Inevitably someone will want to support VXLAN or other UDP
encapsulations in flow dissector. The only correct way to do this is
going to be to do a lookup on UDP socket and have a flow_dissector
function related to the socket. This is the model for dealing with UDP
encapsulations in GRO that could be extended for flow dissection. We
cannot hard code port numbers in flow_dissector. The interesting part
here will be making a robust interface to avoid the pitfalls we've
seen in some of the protocols in flow_dissector.

- Allow calling a BPF function to do custom flow dissection. IIRC
there someone (Daniel?) had already implement flow_dissector in BPF
with pretty good results.

How will this help us for cls_flower case? Are you suggesting to put this
whole BPF occult to the next level and use it kernel-to-kernel? :D